Inkjet printing is well suited to the SOHO (small office, home office) printer market. Increasingly, inkjet printing is expanding into other markets, such as label and wideformat printing. Wideformat inkjet printing is attractive for printing onto a variety of media substrates, ranging from corrugated cartons and pizza boxes to display posters.
As used herein, the term “wideformat printer” refers to any printer capable of printing onto media widths greater than A4 size i.e. greater than 210 mm (8.3 inches). Usually, wideformat printers are configured for printing onto media widths of up to 36 inches (914 mm), up to 54 inches (1372 mm) or greater.
Conventional wideformat inkjet printers are characterized by their slow print speeds. In a conventional wideformat inkjet printer, the printhead traverses back and forth across the width of the media in swathes to produce a printed image. To some extent, the slow speeds and cost of printing has limited the uptake of wideformat inkjet printers.
The Assignee's Memjet® pagewide printing technology has revolutionized the inkjet printing market. Pagewidth printers employ one or more fixed printhead(s) while the print medium is fed continuously past the printhead(s). This arrangement vastly increases print speeds. Hence, wideformat printers manufactured using the Assignee's pagewide printing technology are gaining increasing fraction in the wideformat market.
US2011/0025748, the contents of which are herein incorporated by reference, describes a wideformat printer based on the Assignee's pagewidth printing technology. This printer employs a plurality of fixed printheads staggered across the page and a media feed mechanism configured for aligning print media with the printheads as the print media are fed continuously past the printheads in a single pass.
One of the challenges of high-speed wideformat printing, where print media are fed past the fixed printhead assembly at speeds of 6 inches per second or greater, is maintaining accurate registration of the print medium with the printhead assembly. In particular, the print medium should be uniformly flat and travelling at a known velocity as it passes through the print zone. Any variation in flatness or velocity potentially causes a deterioration in print quality.
The known media feed system described in US2011/0025748 comprises a drive (“grit”) roller upstream of the print zone, a fixed vacuum platen in the print zone opposite the fixed printhead assembly, and a vacuum belt assembly downstream of the print zone. The vacuum belt assembly and the drive roller are coordinated via a print engine controller to maintain accurate registration of the print medium with the printhead assembly as it passes through the print zone.
One of the problems of pagewidth printing, which is particularly exacerbated in wideformat printing, is media buckling or ‘tenting’. Media buckling is a term used to describe a print medium which is not uniformly flat; in other words, a print medium having ripples which result in a varying height of the media surface relative to the printhead(s). Media buckling generally causes a loss of print quality. In a worst case scenario, media buckling causes the print medium to buckle into contact with the printhead(s) and cause a severe loss of print quality.
In the printer described in US2011/0025748, a relatively small degree of skew in the downstream vacuum belt assembly can generate buckling in print media and, as a consequence, produce visible artifacts in the printed image. In practice, it is difficult to manufacture a vacuum belt assembly having perfect parallel of alignment of the vacuum belt(s) with the media feed direction. For example, microscopic eccentricities in the shafts or pulleys supporting the vacuum belts can produce small deviations in the travel direction of the belts. These deviations are transferred to the print medium engaged with the belts and tend to amplify over the duration of a print, thereby causing media buckling and loss of print quality.
It would be desirable to provide a printer having a media feed mechanism, which minimizes the extent of media buckling and provides improved print quality. It would be particularly desirable to improve the media feed mechanism described in US2011/0025748 so as to minimize media buckling.